Auxiliary bass radiator units

ABSTRACT

An auxiliary bass radiator unit is disclosed for mounting in an aperture in a loudspeaker enclosure. The unit comprises a substantially rigid panel member ( 10 ) mounted on a flexable surround member ( 12 ) so as to allow the panel member, when mounted, in use, in the aperture to move in sympathy with sound waves within the enclosure. The flexable surround member includes a hinge portion ( 14 ) mounting the panel member for movement as a hinged flap. Thus, movement of the panel member in twisting and other undesirable modes is substantially avoided.

This invention relates to auxiliary bass radiator units. That is to say,units which when installed in a loudspeaker enclosure form an auxiliarybass radiator.

Auxiliary bass radiators (ABRs) have been known for many years and areused to take the place of tuning ports in bass reflex loudspeakerenclosures.

A bass reflex loudspeaker enclosure, which is a fourth order acousticsystem, has the bass output augmented by the Helmholtz resonance thatoccurs when the mass of the air in a tuning port resonates on thestiffness of the air inside the box. Generally, if such a system isdesigned properly, about half an octave of extra bass extension may beachieved by this means. The roll off rate for a fourth order, bassreflex. system is 24 dB per octave below the resonance frequency. For aclosed loudspeaker enclosure with no tuning port, the rate is 12 dB peroctave.

ABRs were devised to allow low frequency Helmholtz tunings to beachieved when physically small loudspeaker enclosures were needed. Insuch cases, the length of a non-ABR tuning port would be too long to beaccommodated in the enclosure and would have troublesome pipe resonancesof its own. An equivalent resonance frequency can, however, be achievedby replacing the mass of air in the tuning port with a solid mass on aseparate suspension. Such an arrangement is effectively a loudspeakerdiaphragm without either voice coil or magnet. By choosing the mass tomatch the diaphragm area and size of the enclosure, this mass springresonator may be tuned to virtually any frequency desired in practicewithout the problems of length from which tuning ports suffered.

Usually, the free air resonance frequency of an ABR is made as low aspossible and then, when it is placed in the enclosure, the stiffness ofthe air in the enclosure takes over as the major stiffness tuningfactor. The combination of an ABR and enclosure has a response verysimilar to that which would have been achieved with a non-ABR tuningport.

If, however, the free air resonance is made too high, a dip occurs inthe output of the system at the free air resonance frequency and thebass roll off rate is steeper above this free air resonance dip.

It is an object of the invention to provide an improved auxiliary bassradiator unit.

The present invention provides an auxiliary bass radiator unit formounting in an aperture in a loudspeaker enclosure, the unit comprisinga substantially rigid panel member mounted on a flexible surround memberso as to allow the panel member, when mounted, in use, in the saidaperture, to move in sympathy with sound waves within the enclosure,wherein the panel member is constrained to move as a hinged flap.

The invention is based on the realization that because ABRs had to bemade to allow a long throw, that is a large movement back and forth, tooccur at the mass spring or Helmholtz equivalent resonance frequency,they unfortunately allowed the ABR panel member to move in other modesthan simply back and forth. For example, rocking and twisting modes werenot prevented from occurring by the necessarily floppy suspension. Thesehigher order modes coloured the resulting sound output from the speakersystem.

In the construction according to the invention, the said higher ordermodes are substantially suppressed. The constraint substantiallyprevents rocking, twisting and other undesirable modes of vibration fromoccurring.

Advantageously, a hinge portion is included within the flexible surroundmember and mounts the panel member for movement as a hinged flap. Such aconstruction provides a simple way of constraining the movement of thepanel member.

Advantageously, the outer periphery of the surround member is connectedto a substantially rigid frame member for mounting the flexible surroundmember in the said aperture. Such a construction facilitates themounting of the periphery of the surround member in the said aperture.

Preferably, the frame member includes a sealing bead of resilientmaterial to seal the frame member in the said aperture. By this means, agood seal between the frame member and the aperture can readily beachieved.

Advantageously, the panel member includes a substantially straight sidealong at least part of which the hinge portion is provided. Such aconstruction is particularly simple.

The hinge portion may be defined by an integral part of the surroundmember. In particular, the hinge portion may comprise a flat web portionof the surround member.

Advantageously, the web portion is connected to an edge portion of thepanel member and to a corresponding edge portion of the frame member andfurther includes an integral spur extending the flat web portion into aT-shaped cross-section, the spur being located between the edge of thepanel member and the edge of the frame member. Such a constructionprovides a particularly effective form of hinge.

At locations other than in the hinge portion, the surround member maycomprise a roll portion. The roll portion provides a simple means ofmounting the free edges of the panel member.

Preferably, the roll portion tapers towards the hinge portion. By thatmeans, greater movement at distances remote from the hinge portion isreadily accommodated.

The roll portion may be of semi-circular cross-section.

Advantageously, the roll portion includes transverse ribs. By thismeans, any tendency of the surround member to pucker can be reduced.

Preferably, the ribs are formed by corrugations in the material of thesurround member.

The panel member may have a plurality of substantially straight sidesalong one of which the hinged portion is provided.

The ribs may be provided at one or more corners, remote from the hingedportion, where two straight sides meet.

Advantageously, the said one or more corners are rounded. By this meansalso, any tendency to puckering can be reduced.

The panel member may be substantially rectangular with rounded cornersat its end opposite to the hinged portion.

A short side of the rectangular panel member may have the hingedmounting.

The surround member may be made of resilient polymeric material, forexample, a natural or synthetic rubber material.

The panel member may be made of plastics material, for example,polypropylene.

The frame member may be made of plastics material, for example,polypropylene.

The unit may be made by the co-injection moulding of component parts.

The panel member, when at rest, may be set back substantially from thesurface of the frame member.

The panel member may have a thickness of at least 3 millimetres, or ofat least 4 millimetres, or of at least 5 millimetres, or a thickness ofbetween 4 and 10 millimetres. Such dimensions enable the panel member tohave sufficient mass and stiffness to be used without the addition of asupplementary weighting or stiffening means.

The invention also provides a loudspeaker enclosure including anauxiliary bass radiator unit according to the invention.

Two such units may be provided on opposite sides of the enclosure. Bythis means, the physical stability of the enclosure when in use isimproved.

The invention also provides a loudspeaker system comprising an enclosureas defined above and one or more loudspeaker drive units.

An auxiliary bass radiator unit constructed in accordance with theinvention will now be described, by way of example only, with referenceto the accompanying drawings, in which:

FIG. 1 is a perspective view of a loudspeaker enclosure including twosuch auxiliary bass radiator units;

FIG. 2 is a perspective view of the auxiliary bass radiator unit;

FIG. 3 is an elevational view of the auxiliary bass radiator unit;

FIG. 4 is a cross-sectional view taken on the line IV—IV marked in FIG.3;

FIG. 5 is a view seen in the direction of the arrow V marked in FIG. 4;

FIG. 6 is a view seen in the direction of the arrow VI marked in FIG. 4;

FIG. 7 is a cross-sectional view taken on the line VII—VII marked inFIG. 3;

FIG. 8 is a side elevation corresponding to FIG. 4; and

FIG. 9 is a detail view to an enlarged scale of a part of FIG. 4.

Referring to the accompanying drawings, FIG. 1 shows a loudspeakersystem 1 comprising an enclosure 2, a bass and lower mid-rangeloudspeaker drive unit 3, a high-frequency loudspeaker drive unit 4, anupper mid-range loudspeaker drive units 6, and two auxiliary bassradiator units of which only one, 8, is seen in the drawing. The otherauxiliary bass radiator unit (not shown) is constructed and arranged asa mirror image of the unit 8 on the side of the enclosure 2 not visiblein the drawing.

Each auxiliary bass radiator unit is mounted in an aperture in theloudspeaker enclosure 1 and comprises a substantially rigid panel member10 mounted on a flexible surround member 12 so as to allow the panelmember to move in sympathy with sound waves within the enclosure. Thepanel member 10 is made of plastics material, preferably polypropylene.

The flexible surround member 12 includes a hinge portion 14 mounting thepanel member 10 for movement as a hinged flap. The surround member 12 ismade of resilient polymeric material, preferably, synthetic rubbermaterial.

The outer periphery of the surround member 12 is connected to asubstantially rigid frame member 16 for mounting the flexible surroundmember in the enclosure 1. The frame member 16 is made of plasticsmaterial, preferably, polypropylene.

The frame member 16 includes a sealing bead 20 of resilient material toseal the frame member in the said aperture.

The panel member 10 includes a substantially straight side 22 alongwhich the hinge portion 14 is provided.

As can be seen in the drawings, the panel member 10 is substantiallyrectangular with rounded corners 40 and 43 at its end opposite to thehinged portion 14, a short side (22) of the rectangular panel having thehinged mounting.

The hinge portion 14 is defined by an integral part of the surroundmember and comprises a flat web portion 24 of the surround member. Theweb portion 24 is connected to a reduced thickness edge portion 26 ofthe panel member 10 and to a corresponding reduced thickness edgeportion 28 of the frame member 16. The web portion 24 further includesan integral spur 30 extending the flat web portion into a T-shapedcross-section, the spur being located between the edge portion 26 of thepanel member 10 and the edge portion 28 of the frame member 16.

At locations other than in the hinge portion 14, the surround member 12comprises a roll portion 32. The roll portion 32 tapers towards thehinge portion and the roll is of semi-circular form and includestransverse ribs 34 and lip portions 36 and 38. The lip portions 36 and38 are connected to the panel member 10 and the frame member 16respectively.

The ribs 34 are formed by corrugations in the material of the surroundmember 12 and are provided at corners 40 and 42, remote from the hingedportion 14.

The unit is made by co-injection moulding of the component parts 10(panel member), 12 (surround member) and 16 (frame member). As can beseen in FIG. 1, the panel member 10, when at rest, is set backsubstantially from the surface of the frame member

Three mounting eyes 50 are provided, each to receive a respectivemounting screw (not shown).

Thus, each auxiliary bass radiator 8 has a hinge along one edge and sodefines a flap that can move back and forth. This construction preventsmany of the troublesome upper frequency resonances which tended to occurin a conventional “freely floating” auxiliary bass radiator.

The completely floppy surround conventionally used is here replaced witha hinge along one side of the auxiliary bass radiator panel member. Thepanel member has at least one straight edge to facilitate the operationof the hinge but the rest of the panel member may be of virtually anyshape. The surround member is arranged to allow increasing movement asdistance from the hinged edge increases. Thus, instead of an in-outpiston like motion occurring, the present hinged construction remainseffectively stationary at the hinged edge and, at any given frequency,the movement in and out in a flapping motion increases linearly asdistance from the hinge increases.

The fundamental frequency of the present hinged auxiliary bass radiatorscan be altered in the same way as with any other auxiliary bass radiatorby changing the mass per unit area or the stiffness of the surround. Asusual the free air resonance of the auxiliary bass resonator willusually be made as low as possible to avoid a dip in the frequencyresponse resulting from the free air resonance of the auxiliary bassradiator resonating on its own suspension.

The panel member itself is very stiff and well-damped to avoid panelresonances occurring within the panel member itself. Rocking andtwisting modes are largely prevented by the hinge mechanism.

As an example only, some preferred dimensions will now be given.

The following table gives the dimensions in millimetres of lengthsmarked in FIG. 3:

a 47.2 b 130.0 c 145.9 d 7.3 e 67.5 f 0.75 g 49.4 h 6.2 i 9.9 j 1.0

The following table gives the radius in millimetres of curves marked inFIG. 3:

k 8.0 q 1.8 l 18.0

The following table gives the magnitude in degrees of angles marked inFIG. 3:

m 7.2 n 8.5 o 2.0 p 16.0

The following table gives the dimensions in millimetres of lengthsmarked in FIG. 4:

a 1.0 b 1.0 c 0.5 e 1.5 f 2.0 g 3.6 h 5.0 i 68.5 j 39.4 l 4.0 m 18.0 q6.0 v 0.9

The following table gives the radius in millimetres of curves marked inFIG. 4:

d 1.5 k 25 o 21.0 p 22.4 s 25.7 u 1.5

The following table gives the magnitude in degrees of angles marked inFIG. 4:

n 72.3 r 3.0 t 13.0

The following table gives the dimensions in millimetres of lengthsmarked in FIG. 6:

a 55.0 b 55.0

The following table gives the diameter in millimetres of circles markedin FIG. 6:

c 8.5 d 4.1

The following table gives the dimensions in millimetres of lengthsmarked in FIG. 7:

a 1.1 b 2.4 c 2.9 d 0.5

The following table gives the radius in millimetres of curves marked inFIG. 7:

e 0.25 f 2.3 g 1.5

The following table gives the dimensions in millimetres of lengthsmarked in FIG. 8:

b 10.9 c 7.3 d 4.3 f 83.2 g 80.1 h 7.6 i 6.0

The following table gives the radius in millimetres of curves marked inFIG. 8:

j 22.4 k 28.7

The following table gives the magnitude in degrees of angles marked inFIG. 8:

a 14.5 e 8.0 l 14.5 m 6.1 n 8.4

The following table gives the dimensions in millimetres of lengthsmarked in FIG. 9:

a 0.5 b 0.5 c 10.0

The following table gives the radius in millimetres of curves marked inFIG. 9:

d 0.25 e 4.01

The angle f marked in FIG. 9 is 3.0 degrees.

Many different variations of the illustrated construction are possiblewithout departing from the scope of the invention defined by theappended claims. For example, the panel member can have a weightattached to it to increase its mass and, provided that it mounted tomove as a hinged flap can have virtually any shape. The rigid framemember can be omitted and the flexible surround member secure directlyto the loudspeaker enclosure. A discrete hinge member can be used inplace of or in addition to the integral hinge member.

An auxiliary bass radiator of which the substantially rigid panel memberis in the form of an oval with two parallel sides can be provided with ahinge portion along one of the two parallel sides. In that case, theflexible surround member can comprise a semi-circular roll of which theradius is very much reduced along that side constituting the hingeportion. For example, the roll can have a radius of 1 millimetre alongthe hinge portion side and a radius of 10 millimetres along the otherside.

Virtually any construction which constrains the rigid panel member toflap (like the wings of a bird) as opposed to rock (like a cradle) or tomove back and forth (like a piston) can be employed in an auxiliary bassradiator according to the invention.

An auxiliary bass radiator unit in accordance with the invention can bemade by taking an auxiliary bass radiator unit of conventional form andadding to it a hinge to constrain the rigid panel member to move as ahinged flap.

What is claimed is:
 1. An auxiliary bass radiator unit for mounting inan aperture in a loudspeaker enclosure, said unit comprising asubstantially rigid panel member mounted on a flexible surround memberso as to allow said panel member mounted in said aperture to move insympathy with sound waves within said enclosure, wherein said panelmember is constrained to move as a hinged flap whenever it moves.
 2. Anauxiliary bass radiator unit as claimed in claim 1, wherein a hingeportion is included within said flexible surround member to mount saidpanel member for movement as a hinged flap.
 3. A unit as claimed inclaim 2, wherein the outer periphery of said surround member isconnected to a substantially rigid frame member to mount said flexiblesurround member in said aperture.
 4. A unit as claimed in claim 3,wherein said hinge portion is defined by an integral part of saidsurround member.
 5. A unit as claimed in claim 2, wherein said panelmember has a plurality of substantially straight sides along one ofwhich said hinge portion is provided.
 6. A unit as claimed in claim 5,wherein said panel member is substantially rectangular and has roundedcorners at its end opposite to said hinged portion, and a long side ofsaid rectangular panel member has said hinged mounting.
 7. A unit asclaimed in claim 5, wherein the hinge portion is provided along only theone side.
 8. A unit as claimed in claim 2, wherein said hinge portioncomprises a flat web portion of said flexible surround member.
 9. Anauxiliary bass radiator unit for mounting in an aperture in aloudspeaker enclosure, said unit comprising a substantially rigid panelmember mounted on a flexible surround member to allow said panel memberto move in sympathy with sound waves within said enclosure, and a hingeportion included within said flexible surround member mounting saidpanel member for movement as a hinged flap.
 10. A unit as claimed inclaim 9, wherein the outer periphery of said surround member isconnected to a substantially rigid frame member for mounting theflexible surround member in the said aperture, and wherein said framemember includes a sealing bead of resilient material to seal said framemember in said aperture.
 11. A unit as claimed in claim 9, wherein saidpanel member includes a substantially straight side along at least partof which said hinge portion is provided, and wherein said hinge portionis defined by an integral part of said surround member.
 12. A unit asclaimed in claim 11, wherein said surround member has a flat webportion, and said hinge portion comprises said flat web portion of saidsurround member.
 13. A unit as claimed in claim 12, wherein said webportion is connected to an edge portion of said panel member and to acorresponding edge portion of said frame member and further includes anintegral spur extending said flat web portion into a T-shapedcross-section, said spur being located between the edge of said panelmember and the edge of the frame member.
 14. A unit as claimed in claim11, wherein the hinge portion is provided along only the substantiallystraight side.
 15. A unit as claimed in claim 9, wherein at locationsother than in said hinge portion, be said surround member comprises aroll portion.
 16. A unit as claimed in claim 15, wherein said rollportion tapers towards said hinge portion, said roll portion is ofsemi-circular cross-section, and said roll portion includes transverseribs.
 17. A loudspeaker unit comprising: a loudspeaker enclosure, atleast one loudspeaker drive unit mounted in an aperture in saidloudspeaker enclosure, at least one auxiliary bass radiator unit mountedin an auxiliary bass radiator aperture in said loudspeaker enclosure,said auxiliary bass radiator unit comprising a substantially rigid panelmember mounted on a flexible surround member for movement in sympathywith sound waves within the enclosure, said flexible surround memberbeing mounted in said auxiliary bass radiator aperture, and a hingeportion being included within said flexible surround member mountingsaid panel member for movement as a hinged flap.
 18. A loudspeaker unitas claimed in claim 17, wherein the outer periphery of said surroundmember is connected to a substantially rigid frame member, said surroundmember being mounted in said auxiliary bass radiator unit aperture bysaid substantially rigid frame member.
 19. A loudspeaker unit as claimedin claim 18, wherein two of said auxiliary bass radiator units aremounted on opposite sides of said enclosure.
 20. A loudspeaker unit asclaimed in claim 18, wherein said panel member includes a substantiallystraight side along at least part of which said hinge portion isprovided, said hinge portion being defined by an integral part of thesurround member and comprising a flat web portion of the surroundmember, said web portion being connected to an edge portion of the panelmember and to a corresponding edge portion of the frame member andfurther including an integral spur extending said flat web portion intoa T-shaped cross-section, said spur being located between the edge ofthe panel member and the edge of the frame member.
 21. A loudspeakerunit as claimed in claim 18, wherein said surround member comprises aroll portion, said roll portion being of semi-circular cross-section,and including transverse ribs, said ribs being formed by corrugations inthe material of said surround member.
 22. A loudspeaker unit as claimedin claim 17, wherein said panel member is substantially rectangular withrounded corners at its end opposite to the hinged portion, and a longside of the rectangular panel member has said hinged mounting.